Wheel-type abrasive-impelling device



Dec. 9, 1958 w. H. MEAD WHELQTYPE ABRAsIvE-fIMPELLING DEVICE 2Sheets--Sheelzr 1.

File@ oct. 15. i956 FG" mil* United States Patent O f' WHEEL-TYPEABRASIVE-IMPELLING DEVICE William H. Mead, Oakland, Calif. ApplicationOctober 15, 1956, Serial No. 615,856

8 Claims. (Cl. 51-9) This invention relates to a wheel-typeabrasive-impelling device.

Machines in which abrasive is impelled toward a Workpiece from a wheelhave long been known, an example being shown by Linderman in Patent No.2,247,391 tiled July l, 1941. However, quite a few problems haveremained without solution until the present invention solved them.

One object of this invention is to increase the efficiency ofabrasive-throwing wheels by reducing the wear that has been inherent inprior-art abrading wheels. This wear has been caused by the constantfriction of highspeed abrasive particles against the interior surface ofthe wheels and the retention discs used to control the outward tiow ofabrasive. This wear has required constant maintenance and frequentreplacement of parts, even with vaneless wheels.

Another object of the invention is to prevent wear on the interiorsurface of the cup-like wheel itself by providing a structure whichcauses the abrasive to collect in a series of frusto-conical shellssloped along the angle of equilibrium. The disc surfaces aresubstantially covered and remain so, while the additional movingabrasive being fed in simply slides over the relatively stationaryabrasive particles in the steps. In this way, the grit can only wearagainst` itself and not against the wheel.

Another problem solved by this invention relates to the fact that theangle of repose of static granular material is necessarily greater thanthe angle of equilibrium of the s ame material, when centrifugal forceis applied. Because of this fact there has to be some means for axiallyforeshortening the cup of a centrifugal abrasive wheel if the abrasiveis to be fed to the cup by gravity. In other words, if an abrasivematerial whose static angle of repose is 'about 40 is to be fed bygravity into the cup of a wheel, the hopper spout has to slope down atapproximately 45 (or at least greater than 40) or else there will be noflow of abrasive through it. But ifthe radius of the cup is equal to orgreater than its axial length-as it must be in order to get the spoutinto the center of the cup closely adjacent the inner radial wallhow isthe abrasive to be kept from falling off around the entire periphery ofthe wheel? Its angle of repose under the `centrifugal force is arelatively at one as compared with the angle of the static material, say27 as compared with 40. On the other hand, if the axial length of thecup is longer than the radius, how can the abrasive be properly fed bygravity into the cup? The previous approach to this problem has been tospace an annular disc away from the radial wall of the cup andintro-duce the abrasive in between, using the disc to hold it in. Butthis requires another part subject to wear by the abrasive.

Another object, therefore, of the present invention is to provide awheel with an open type of cup design in which the angle of equilibriumcan be balanced with the angle of repose of the static material. This isaccomplished by means of a stepwise construction of the 2,863,261Patented Dec. 9, 1958 cup so that the abrasive, instead of movingradially out to the periphery, is moved in a generally conical path, thesteps being balanced to provide a general resultant slope correspondingto an angle somewhat greater than that of the angle of repose of thestatic material, i. e., about 45, while the angle of repose of theabrasive on each step is the relatively low angle suitable for retainingthe grit on the periphery.

Another important object of the invention is to provide a cup-typeabrasive wheel especially fo-r use with ferromagnetic abrasive particlessuch as steel grit and shot. In this form of the invention a pluralityof coaxial magnet rings of different diameter comprise most or all ofthe axial portion of the steps. The magnets act to control the movementof ferromagnetic particles. Ferromagnetic particles are quite heavy and,when introduced into the center of the cup-type of abrasive wheel, tendto bounce or skip along out to the periphery and then to fall off theedge indiscriminately instead of being taken olf by the discharge means.Thus a great deal of abrasive is wasted. The magnetic rings, which aredescribed in detail below, control these ferromagnetic particles andprevent them from skipping, while the stepwise structure itself servesto prevent lighter particles (such as sand, garnet, walnut shells, andthe like) from skipping when those abrasives are used.

Another object of the invention is to provide a particularly effectivedisposition of magnets in such a wheel.

Another object of the invention is to provide a structure forlpreventing the short-circuiting of the respective magnetic rings. t

Other objects and advantages of the invention will appear from thefollowing description of preferred embodiments of the invention.

In the drawings:

Fig. 1 is a view in front elevation of an abrasiveimpelling wheelembodying the principles of the invention.

Fig. 2 is a view in side elevation and in section of the wheel of Fig.1.

In this invention a wheel or cup 10 is supported for rotation upon ashaft 11 of an electric motor 12, or may be driven by any otherappropriate means. The shaft 11 is attached to `a drive hub 13 which, inturn, is bolted to a radially-extending wall 14 of the cup 10 on theopposite side from the open mouth 15 thereof, thereby leaving theinterior 16 of the cup 10 completely unobstructed. A gravity feed isprovided from a hopper 17 above the cup 1t) through a metering devi-ce18 and conduit 19 into the cup interior 16 and toward the axis 20thereof. Necessarily, this gravity feed lies at an angle greater thanthe angle of repose of the abrasive which, for most suitable materials,means that it may lie at about 45.

The cup 10 is provided with a coaxial series of steps 21. The steps 21near the radial wall 14 are o-f smallest radius, so that the cup 10 isstepped outwardly both radially and axially toward the discharge lip 22of the rim 23. Therefore, as abrasive is fed into the whirling wheel 10and centrifugal force tends to accelerate it towar-d the rim 23, theabrasive moves over the steps 21. The lrst labrasive 24 fed in coversthe steps 21 with a layer of abrasive that subsequently remains staticby virtue of the angle of equilibrium of the material under lthe actionof the centrifugal force. This angle of equilibrium is similar to, butis flatter than, the free angle of repose of the static material. Thus,the radially inner surface of the static abrasive 24 forms on eachsucceeding step a conical frustum, over which subsequent abrasivetravels without any direct contact, except at the edge of the steps 21.

It is apparent that the number of steps 21 may vary to,

in effect, form a true conical surface, but that is not def sirable.From a practical' standpoint, the steps 20 are related to that theeffective angle formed by a line joining their edges is about 45 orgreater, thereby permitting ent-ry of the gravity feed co-nduit 19'. Inother words, the line joining their edgesmust` be greater'than the angleof free repose of the material.

At the periphery suitable discharge means 25 are provided; While thismay be a rotating wheel of the type shown inthe Linderman Patent2,247,391, I prefer to use an air discha-rge means as disclosed in`co-pending appli cation Serial No. 615,972 filed October l5, 1956, or,where steel grit is being used, a permanent magnet (as shown in Figs. 1and 2) or an electro-magnet to draw the material off in a mannerdisclosed and claimed by co-pending application Serial No. 615,842 filedOctober l5, 1956.

The particular form of discharge means 25A forms n'o'partv of thisinvention.

In operation, the abrasive is fed from the hopper 17 through themetering device 18 and conduit 19 down into the wheel and movesoutwardly over the steps 21 to ward the rim 23. The first abrasive fedinforms an initial layer 24 that remains substantially static, while thesubsequent abrasive travels over that abrasive and -does not come incontact with the wheel as it moves out to the periphery 22, where it istaken off the wheel 10 by the discharge device 25.

As stated earlier, when steel grit is used, a further control over itsmovement is advisable, since steel Shot and grit are very heavy. Thiscontrol is provided by using magnetic rings Stb as the axial portion ofeach step 21. Each ring magnet 30 may be cast as a unit or formed from aseries of bar magnets, the north poles of all the magnets in one ring3i) facing one axial endof the cup 10 while the south poles face theother end. Somek advantages instrength of field and control may beobtained by reversing the polarity of adjacent rings 30, so that thenorth poles of one ring face the wall 14 and in the next adjacent ringthe south poles face the wall 14, and soon. lt should be noted that themagnetic steps have no relation to whether a magnetic discharge 2.5 isused, but a magnetic discharge may well be used in the same apparatus.

Where magnetic rings 30 are used, it is sometimes desirable to preventwhat may be desc-ribed as a short-circuit of the magnet due to the steelparticles being inA direct contact with the magnetic rings 3213.Avoidance of this and strengthening of the field in general may beprovided by providing a covering 31 of plasteraof-Paris,

brass, or other nonmagnetic material over each ring 3i) to provide agenerally frusto-conical surface, preferably somewhat concave, whoseangle is somewhat flatter than that of the angle of equilibrium of theabrasive. Then the layer of ferromagnetic abrasive deposits over thecovering 31 and protects its surface from the movingv particles of grit,which thus move only over the surface of the grit itself. For thispurpose also, radial faces of the magnet rings 3@ are preferablyprotected by overhanging rings 32 of brass or other nonmagneticmaterial. As shown, the overhang is relatively slight but may beextended to any desired degree.

1t is important to obtain control over the ferromagnetic particles fromthe instant they come out of the spout 19. Therefore the innermostmagnetic ring Sil is of rather small diameter and its eld isstrengthened by a plug 35 of magnetic material located along the axisjust opposite the outlet from the feed conduit 19. The space in betweenthe plug 35 and magnet 30 and the area over the plug and magnet arevfilled with a covering 36 like the covering 31. As. the lines 37 ofmagnetic force shown in the drawings illustrate, there is a strongmagnetic field tending' to hold the particles at the center. This tendsto impart to them an angular velocity, whence the centrifugal forceslowly moves them out in a long spiral, with the velocity' of the wheelitself at any given point being 4 l substantially the velo-city of theparticles. The slow outward movement provided by the central plug 3S andthe innermost magnet 30 and by the successive magnetic rings 30 andsteps 21 result in the ultimate in control of ferromagnetic abrasive.

Otherwise, operation of the magnetic device is substantially the same asthat of the regular stepped device, the principal difference being that,since steel grit or shot is the abrasive material being used, themagnetic rings 30 exert a constant control over the abrasive, beginningat the inner portion near the feed conduit 19 and extending out towardthe rim 23. The magnets provide a eld which^is not subject to wear, andthe magnets themselves are protected. The magnetic field acts upon thegrit particles as effectively as baffles or other mechanical parts wouldwithout having any of the disadvantages of mechanical baffles andwithout being subject to wear. The control is substantially complete,and the device can operate indefinitely without wear.

To those skilled in theart to which this invention relates, many changesin construction and widely differing embodiments and applications of theinvention will suggest themselves without departing from the spirit' andscope of the invention. The disclosures and the description herein arepurely illustrative and are not intended to be in any sense limiting.

l claim:

l. A rotating cup-type of abrasive wheel having a series of graduatedannular substantially concentric steps foreshortening the distancebetween the cup and the discharge lip of the cup, and a device forgravity feed of abrasive material into the cup adjacent the axis of itsradial wall, whereby the gravity feed can be inserted into the fore;shortened cup and whereby the wear of abrasive particles o-n the cupsurface is reduced by the building up of 'Substantially static abrasiveparticles at an angle of equilibrium forming a series of conicalfrustums, over the surface of which subsequent particles of` abrasivemove substantially without contact with the surface of the cupv itself.

2. The device of claim l in which the axially extending portions of thestep incorporate magnetic rings, whereby steel grit .abrasive iseffectively restrained from skipping over the surface of the outwardlymoving abrasive.

3. A cup-type of abrasive wheel, having a series of graduated annularsubstantially -concentric steps with the steps of smallest diameteradjacent a radial wall of the cup and those of larger radial diametercloser to the discharge lip of the cup, the angle connecting thedischarge lip with the intersection of the cup and the radial wall ofthe cup, lying at an angle greater than the angle of repose of thematerial; and a device for gravity feed of abrasive material into thecup `adjacent its radial wall, whereby'the gravity feed can be insertedinto the fore'- shortened cup and whereby the wear of abrasive particleson the cup surface is reduced by the building up of substantially'staticabrasive particles at an angle of equilibrium forming a'series of conefrustums over the surface o-f which subsequent particles of abrasivemove without contactingthe surface of the cup itself.

4; The device of claim 3 in which the axially extending portions of thestep incorporate magnetic rings, whereby steel grit abrasive iseffectively restrained froml skipping over the surface of the outwardlymoving abrasive.

5. The device of claim 4 wherein a layer of nonmagnetic material isinterposed between the magnetic rings and the abrasive.

6. The device of claim 4 wherein an axial core lies in-v side the ringof smallest diameter, spaced radially inwardly from it.

7. A rotating cup-type of abrasive wheel, comprising a cup with a radialwall and a cylindrical rim and having a series of graduated annularsubstantially concentric steps with the steps of smallest diameteradjacent a radial wall bf the cup Vand `those of larger radial diametercloser tn a 5 discharge lip `on the rim of the cup, the angle connectingthe discharge lip with the intersection `of the cup and the radial wall`of the cup, lying .at an angle greater than the angle of repose of thematerial, a device for gravity feed of abrasive material into the cupyadjacent its radial wall, whereby the gravity feed can be inserted intothe foreshortened cup and whereby the wear of abrasive particles on thecup surface is reduced by the building up of substantially staticabrasive particles at an angle of equilibrium forming a series of conefrustums over the surface 10 of which subsequent particles of abrasivemove without r contacting the surface of the cup itself, and abrasivedischarge means adjacent said lip.

6 8. The device of claim 7 in which the axially extending portions ofthe step incorporate magnetic rings, whereby steel grit abrasive iseffectively restrained from skipping over the surface of the outwardlymoving abrasive.

References Cited in the tile of this patent UNITED STATES PATENTS2,116,153 Keefer May 3, 1938 2,135,550 Alexander Nov. 8, 1938 2,224,505Unger Dec. 10, 1940 2,247,391 Linderman July 1, 1941 2,323,786 BeiselJuly 6, 1943

